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The Science of Pump Packing

Technological advancements and choosing the right product

reinforced_carbon_pump_packingA lot of end users consider pump packing as being a simple piece of rope with lubricant. What they don’t realise is that the technology behind pump packing is actually far more advanced and complex than a bit of rope dipped in grease.   

Since the phasing out of asbestos from 1970 onwards, there has been significant industry focus on discovering new ways of manufacturing packing in order to make it stronger and more adaptable, with better heat resistance and requiring less flush water.  

Today, contractors have ample choice when choosing a packing solution, whether it be for rotating or static equipment, harsh slurry, gaseous or aquatic environments. It’s no surprise that choosing the right packing for your particular installation, as well as ensuring that it is made from high-grade quality materials is of utmost importance – however as the range of options continues to expand, this choice is becoming more and more difficult.

Advancements in packing

Reduced flush

Older style asbestos or synthetic fibre packing required a lot of flush water to both cool and wash the seal.  However, advancements in material compositions and manufacturing of packing has not only enabled this amount of flush water to be reduced, but has also increased the strength and versatility of packing solutions.

Chesterton has put as much time and research into developing their range of packing solutions as they have with their mechanical seal options, and have been able to develop reinforced packing that requires minimal flush.

In a prominent Australian aluminium refinery, packing on a new Warman pump required 85 litres of flush water per minute. This was an immense amount of water wastage, and the life expectancy of the seal was very poor.

Chesterton removed the old packing and replaced it with their GraphMax solution made from pure graphite mixed with carbon. Once installed, the required flush water amount was reduced to 4-6 litres per minute.

Increased strength

The reinforcement of packing materials is the key to increased strength and product versatility.

Initially, the problem with graphite packing was that it is very weak in its pure form. This meant that it was only able to be used in either steam applications, or reinforced with wire jackets for high pressure applications.

Although this technology is still commonly used, advances in wire braiding designs are providing the industry with stronger alternatives for static equipment. Examples of these from the Chesterton range include the Chesterton 1600, 1601 and the new low emission packing 1622. Reinforcement with wire jackets is not an option in rotating equipment however, as there is always the risk that the wire will become exposed and make contact with the shaft, resulting in wear.

To combat graphite’s poor strength, Chesterton began braiding carbon yarn at strategic points within the packing. An example of this is the Graphmax and 1830SSP. These products now have the benefit of graphite’s self lubricating properties, mixed with the strength of carbon. This new braiding technique now enables a single type of pump packing to be used in both static as well as rotating equipment, including the pumping of harsh slurry or chemicals.

graphmax_largeYou get what you pay for

There are many poor quality versions of packing on the market where, unfortunately, the only apparent difference is the cost. These cheap versions can look and feel very similar to higher quality packing, as they can be made from the same fibre and even have similar blocking agents and lubricants.  However, the volume of lubricant, as well as the quality of the fibre is what makes these cheaper packing solutions poor performers once installed.

Packing for rotating equipment

The key to choosing the right packing for your rotating equipment comes down to the packing’s ability to disperse lubricant onto the dynamic surface (shaft). If this runs dry, a build up in friction and subsequent heat generation will take place causing shaft and sleeve wear. The more the sleeve wears, the shorter the lifespan of the packing. You will see example of this in lower grade packings. This is common among cheaper packing products, as the volume of lubrication mixed into the fibre is a lot less.

An example of this, is low grade graphite packing. Typically, graphite packing is a very effective sealing solution for rotating equipment, as graphite itself is a natural lubricant. However, many cheaper graphite packing solutions are mixed with fillers and binders or are made from lower grade graphite with a high ash content. This results in poorer lubrication, and reduced strength.

Packing for static equipment

Choosing a packing with minimum volume loss once installed is the best packing solution for static equipment. If volume is lost, the actual load on the seal needs to be increased for the packing to continue to make an effective radial seal. Teflon packing for valves is a good option as very little volume is lost once it has been tightened, however Teflon does have its limitations, particularly in regards to its temperature capability that has a maximum of 240˚C. Packing made from pure graphite is also a fantastic option as it is self lubricating without volume loss.

Product lifecycle cost effectiveness

A lower acquisition cost when it comes to pump and valve packing is not always the most cost effective. Cheap packing solutions made from low grade materials simply do not have the life expectancy of good quality packing. Although high quality packing may be two to three times more expensive, it is important to consider the overall lifecycle costs of your pump or valve. Repairs to pump packing can cause major equipment downtime, not to mention the high repair and replacement costs if the packing fails. These repair costs can quickly wipe away any savings made from your initial purchase, and end up costing you much more in both time and money.

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